Dev: Refector _fnGetDataMaster and _fnClearTable to be shorter and clearer
New: $, clear, settings, on, one and off methods for new API

- $ - perform a jQuery selector on the nodes in the table (matching the
  $ method from the old API).

- clear - clear the table completely (replaces fnClearTable).

- settings - get an array of the settings objects for the tables used in
  the API instance.

- on - jQuery event listener proxy. Use for table specific events
  ('draw', 'xhr' etc).

- one - jQuery event listener proxy (single event).

- off - jQuery event unlistener proxy.
Dev: Tidy up new `settings()` method, doesn't actually need an iterator